The Art of Asteroid Avoidance

Just what can a little spacecraft do to deflect an asteroid – a lot say some scientists. Credit: SpaceDaily

Col. Gen. Vladimir Popovkin, commander of the Russian Military Space Forces, told a news conference Friday that the national satellite network lacked a spacecraft capable of preventing an asteroid strike.

He also said chances of such a collision were infinitely small, and it was inexpedient to spend huge sums on neutralizing this unlikely threat. Still, the general might be underestimating the scale of the asteroid threat.

Over the last few decades there has been a great deal of debate about the level of danger posed by impacts from asteroids and comets. It appears the world needs to take the threat of asteroid strikes a lot more seriously.

Astronomers have already spotted about 800 asteroids, solid rocky celestial bodies, with a diameter of over 1,000 meters (3,250 feet) moving along circumsolar elliptical orbits. However, there may be as many as 2,000 large asteroids, and some 135,000 rocks with a diameter of 100 meters (325 feet) and more.

It should be noted that asteroid orbits are unstable and tend to change under the influence of gravitational fields of the terrestrial planets – Mercury, Venus, Earth and Mars.

An asteroid, which flashed past our planet at a distance of 5 million kilometers (3.1 million miles) in November 1996, returned in September 2004 and flew by just 1.5 million kilometers (930,000 miles) from Earth’s surface. In March 1989, a 300 meter (975 foot) asteroid crossed the terrestrial orbit and missed the Earth by just six hours. Astronomers spotted the rock only when it was receding into space.

Impact of the Tunguska explosion is visible even after 90 years. Credit: Galena HS

An asteroid measuring over 1,000 meters in diameter is potentially capable of destroying human civilization. Chances of a major asteroid impact in the 21st century are a mere 0.0002 percent, although there is a 2 percent probability of Earth colliding with a 100 meter asteroid before the year 2100.

The blast would equal to 100 Megatons in trinitrotoluol equivalent, and it would kill millions of people if it hit a populous industrial region harboring many hazardous enterprises.

Scientists are quite alarmed, because they register additional asteroids buzzing the Earth. Spaceguard Survey, an international service responsible for detecting and tracking potentially dangerous space objects, has now been established.

Russia established the Space Shield Foundation east of the Urals. The organization involved scientists from the Snezhinsk (Chelyabinsk-70) nuclear center and the Makeev State Rocket Center in Miass. The foundation eventually set up subsidiaries in Novosibirsk and Korolev, outside Moscow.

The Planetary Defense Center, which was established in Russia three years ago, comprises the best defense-industry facilities, aerospace enterprises, in the first place, as well as academic and sectoral research.

Scientists say the best way to cope with the asteroid problem is to register and observe all potentially dangerous space objects. However, it is not enough to spot an asteroid, because most of them have unstable orbits; consequently such asteroids may disappear later on.

Every terrestrial hemisphere must therefore have three or four telescopes with primary mirrors 4 meters to 5 meters in diameter for observing asteroids round the clock. Such observations would make it possible to catalog asteroids with a diameter of less than 1,000 meters.

Too close for comfort. Credit: ESA

Many observatories – Russian observatories included – are now working on the asteroid catalog. Scientists claim that it would become possible to warn about impending asteroid strikes 80 to 100 years in advance if 90 percent of asteroids are registered, and in case of regular observations. But long-term asteroid protection remains in the realm of science fiction.

Two scenarios exist for shielding this planet from a dangerous space object. First, any hostile object can be shattered in deep space, before it reaches Earth. Second, its orbit can be changed, so the asteroid steers clear of our planet.

Some scientists think a nuclear device could be detonated on the asteroid’s surface or in direct proximity to it, making it possible either to shatter that asteroid, whose fragments may still threaten Earth, or heat up one of its sides and vaporize large segments, thereby changing the asteroid’s flight path. Technically speaking, a powerful nuclear explosion can change the orbit of the asteroid several months before it impacts the planet.

Russian scientists suggest using the kinetic energy of asteroids in order to destroy them. This can be accomplished by creating an artificial dust cloud in the asteroid’s path. That cloud’s particles would interact with the asteroid surface and gouge craters.

The dangerous object would finally disintegrate because the mass of crater particles would be directly proportional to the kinetic energy of colliding bodies. The United States demonstrated this effective method on July 4, 2005, when part of the Deep Impact spacecraft, a copper ball, 65 centimeters (about 3 feet) in diameter and weighing 140 kilograms (300 pounds) hit the comet Tempel 1, an object with a radius of 3 kilometers (1.9 miles) and carved a 200 meter crater.

It would be much harder to build a catapult with the help of robots on the asteroid’s surface for launching rocks into space and altering the asteroid’s trajectory. A rocket engine on the asteroid’s surface likewise could change its flight path. Both options present problems, because of the precision needed to deflect an asteroid correctly.

An aerial view of Meteor Crater, Arizona. Credit: Jim Hurley, 1978

Another method suggests using laser or solar beams to heat up a small asteroid-surface section and to propel it in the required direction. But it would be difficult to deliver a laser unit or a mirror-lens to the asteroid and to ensure the required attitude control for a long time.

An asteroid patrol would prove quite expensive; consequently, it would be expedient to streamline its elements during current space programs, which is being done. The Deep Impact project shows scientists are working in the right direction.

Russia’s Lavochkin NPO has suggested the demonstration project Space Patrol for perfecting various asteroid-protection methods and systems. A small spacecraft with a mass of just 200 kilograms, now being developed within this project’s framework, would act as navigator or pilot and could liftoff atop converted ballistic missiles such as the Strela and the Rokot.

The European Space Agency also is working on its Don Quijote mission, intended to investigate the possibility of deflecting a dangerous asteroid. A Russian Soyuz-Fregat rocket would launch the Sancho and Hidalgo spacecraft, which would reach the asteroid within six or seven months.

Sancho would be the first to arrive at its destination, taking position in orbit around the asteroid. Hidalgo eventually would slam into it at 10 kilometers per second (22,300 miles per hour). Sancho would then inspect the damaged asteroid and assess its changed trajectory. ESA will select the target asteroid in 2007, and Sancho and Hidalgo are scheduled to lift off in between 2010 and 2015.